An optical head device irradiates an optical disk with laser lights and detects its reflection lights, to thereby read information recorded in pits formed on a surface of the optical disk.
In the optical head device, laser lights having different wavelengths are emitted according to the type of optical disk. For example, laser lights having a wavelength band of 405 nm are used in HD-DVDs (High Definition Digital Versatile Disk) or BDs (Blu-ray Disk), laser lights having a wavelength band of 660 nm are used in DVDs (Digital Versatile Disk), and laser lights having a wavelength band of 785 nm are used in CDs (Compact Disk). Thus, in order to correspond to different types of optical disks with a single optical head device, it is necessary to mount a laser device which oscillates a wavelength according to the optical disk to the device.
In recent years, for miniaturization of the optical head device, a two-wavelength laser source has been used in which a semiconductor laser which emits laser lights having a wavelength band for DVDs and a semiconductor laser which emits laser lights having a wavelength band for CDs are formed in a single chip. Patent Document 1 discloses a diffraction grating which can be applied to such a light source. Further, Patent Document 2 discloses a phase correction device which is disposed in an optical path of three wavelengths and corrects a phase in a wavelength selecting manner.